1. Field of the Invention
The invention relates to a heat storage apparatus that effectively warms up an engine.
2. Description of the Related Art
When warming-up has not been completed, for example, great friction is caused in an engine. Therefore, the warming-up needs to be quickly completed. In particular, components having slide portions, such as cylinder bores, pistons, and a crankshaft, need to be quickly warmed to efficiently operate the engine. In an ordinary engine, when air-fuel mixture starts to be ignited in the cylinder, engine components such as a cylinder block and a cylinder head, and engine oil that is circulated in oil passages formed in the engine components are warmed. Thus, the warming-up gradually proceeds. For example, Japanese Patent Application Publication No. 11-182393 (JP-A-11-182393) describes a quick warming-up apparatus for an engine, in which a latent heat storage material (heat storage agent) is housed in a heat storage material chamber that is formed to surround cylinders to quickly complete warming-up of the engine. In the quick warming-up apparatus, voltage is applied to the heat storage agent in the supercooled state during the cold start of the engine. Thus, the phase of the heat storage agent starts to be changed, and latent heat is released.
In such a quick warming-up apparatus for an engine, the temperature of the heat storage agent is detected by a temperature sensor; the detected value of the temperature of the heat storage agent is referenced; and the state of the heat storage agent is determined based on the record of the temperature of the heat storage agent after the heat storage agent releases heat, to avoid unnecessary application of the voltage and unnecessary release of heat. More specifically, the amount of heat received by the heat storage agent is estimated, based on, for example, the sum of time periods during which the temperature of the heat storage agent is equal to or above the melting point, or the sum of products of values of the temperature of the heat storage agent that are equal to or above the melting point and time periods during which the temperature of the heat storage agent is equal to or above the melting point when the engine is operating. Based on the amount of heat received by the heat storage agent, it is determined whether heat is stored in the heat storage agent, as latent heat. Based on such a determination, a control is executed to prevent the application of the voltage when the heat storage agent has not been returned to a heat storage state, that is, when heat is not stored in the heat storage agent. The temperature sensor, which detects the temperature of the heat storage agent, is installed in the heat storage material chamber.
Japanese Patent Application Publication No. 1-181091 (JP-A-1-181091) also describes a similar technology in which the state of a heat storage agent is determined. The heat storage apparatus described in this publication includes a latent heat storage material (heat storage agent); a heat storage tank containing the heat storage agent; temperature detection means for detecting the temperature of the heat storage agent; vapor pressure detection means for detecting the pressure of vapor in the heat storage tank; and control means for determining whether the heat storage agent is in the supercooled state, by comparing the pressure of saturated vapor determined based on the temperature of the heat storage agent detected by the temperature detection means, and the pressure detected by the vapor pressure detection means.
In the quick warming-up apparatus for an engine described in the publication No. 11-182393, it is possible to avoid, for example, unnecessary application of the voltage by determining the state of the heat storage agent. In the heat storage apparatus described in the publication No. 1-181091, it is possible to accurately determine whether the heat storage agent is in the supercooled state, by comparing the pressure of saturated vapor determined based on the temperature of the heat storage agent, and the pressure detected by the vapor pressure detection means.
However, in each of the quick warming-up apparatus for an engine described in the publication No. 11-182393 and the heat storage apparatus described in the publication No. 1-181091, the temperature sensor for detecting the temperature of the heat storage agent needs to be separately provided. Therefore, it costs much to newly prepare the temperature sensor, and to install the temperature sensor. Also, it is necessary to take measures to prevent a leak of the heat storage agent in the portion where the temperature sensor is installed. This also increases the cost.